The present invention relates to a fluid pressure device of the inner gearing type comprising an outer gear having circumferentially arranged external teeth and an inner gear eccentrically disposed relative to the outer gear and having circumferentially arranged internal teeth in meshing engagement with the external teeth of the outer gear, wherein one of the gears which acts as a rotor rotates around its own axis while making an orbital movement around the axis of the other gear which works as a stator so that expandable and contractable fluid working chambers are formed between the meshing teeth of the gears. The present invention relates more particularly to a torque transmission mechanism between the rotor and the output shaft or input shaft associated with the rotor in a fluid pressure device of the kind stated above.
In the fluid pressure device of the kind described, only the rotation of the rotor around the axis thereof is taken out while cancelling the orbital movement to drive the output shaft. Alternatively, the rotation of the input shaft is transmitted to the rotor to cause the orbital movement and rotation of the rotor. In a conventional fluid pressure device of the kind described, the transmission of torque between the rotor and the output or input shaft is made by a mechanism which incorporates a drive shaft inclined with respect to the axes of the rotor and the output or input shaft and splined at both ends thereof to the rotor and the shaft.
FIG. 1 illustrates a fluid pressure device having a torque transmission mechanism of the above-explained type, used as a hydraulic motor. This hydraulic motor is generally composed of three sections: namely, an output mechanism section a', displacement chamber section (fluid working chamber section) b' and a valve mechanism section c'. The transmission of torque between the output mechanism section a' and the displacement chamber section b' is made through a drive 1', while the transmission of torque between the displacement chamber section b' and the valve mechanism section c' is made by means of a valve switching drive 2'. To this end, each of the drive 1' and the valve switching drive 2' is provided with splines at both ends thereof. The output section a' is composed of an output shaft 4' having internal splines in engagement with splines of the drive 1', housing 5' and bearings 6' supporting the output shaft 4' and is arranged to transmit the output to a driven machine while bearing the external load. The displacement chamber produces an orbital movement of an outer gear 3' simultaneously with the rotation of the outer gear 3' around the axis thereof. The drive 1' transmits only the rotation of the outer gear 3' to the output shaft 4' while cancelling the orbital movement.
On the other hand, the valve mechanism section c' has a valve 7' having internal splines in engagement with splines of the valve switching drive 2', valve plate 9' which is fixed to a ring 8' and arranged to switch the passage of the pressurized oil in cooperation with the valve 7' and a valve housing 10'. The valve switching drive 2' transmits only the rotation of the outer gear 3' to the valve 7' to rotate the latter while cancelling the orbital movement. The function of the valve mechanism section c' is to distribute the pressurized oil from the pump to the displacement chambers 11' while collecting the oil returning from the latter.
As will be seen from FIG. 2, in the displacement chamber section b', the teeth of an inner gear 12' have an arcuate profile constituted by rollers 13' while the teeth of the outer gear 3', gearing with the teeth of the inner gear 12', have a trochoidal (epitrochoid parallel curve) profile. The number of the teeth of the outer gear 3' is smaller by one than the number of the teeth of the inner gear 12'. The axis 14' of the inner gear and the axis 15' of the outer gear are arranged at an eccentricity e with respect to each other. The outer gear 3' and the inner gear 12' define displacement chambers 11' by the points of contact between these gears. The number of the displacement chambers 11' is equal to the number of the teeth of the inner gear 12' which is 7 in the example shown in FIG. 2. In operation, pressurized oil is supplied to the displacement chambers 11' through the valve mechanism section c' so that the displacement chambers 11' repeat expansion and contraction to cause an orbitary movement of the outer gear 3' around the axis 14' of the inner gear simultaneously with the rotation of the outer gear 3' around its own axis 15', thereby to convert the pressure energy of the pressurized oil into torque. This torque is transmitted from the internal splines of the outer gear 3' to the internal splines of the output shaft 4' through the drive 1' so that only the rotation of outer gear 3' is utilized for driving an external load while the orbital movement is cancelled.
The known hydraulic motor of the kind described encounters the following problems due to eccentric orbital movement of the outer gear 3' with respect to the output shaft 4'.
(1) It is necessary to employ a drive 1' provided at both ends with external splines, as well as internal splines in the outer gear 3' and the output shaft 4'.
(2) The meshing between the splines of interconnected members does not meet the theoretical condition of meshing from the view point of mechanics of a gear, since relative eccentric movement is involved between the interconnected members. Therefore, the contact between the splines takes place only over a limited axial length thereof so that the effective contact length of the spline cannot be increased even by an increase of the axial length of the spline.
(3) In order to minimize the influence of the eccentricity, it is necessary to employ a certain minimum distance between the internal splines of the outer gear 3' and the internal splines of the output shaft 4' or the internal splines of the valve 7'.
(4) The diameter of the drive 1' must be selected to be sufficiently small as compared with the diameter of the output shaft, in order that it can make an oscillatory orbital movement within the output shaft 4'.
This type of hydraulic motor advantageously permits the provision of a series of devices having various supply rates only by changing the axial breadth of the displacement chamber section b' without requiring the change of other parts. However, when the supply rate is increased by increasing the breadth of the displacement chamber section b', the motor is obliged to operate only at low pressure because there is a limit in the transmission of the output torque between the splines of the drive 1' and the output shaft 4'.
In order to obviate the above-described problems, it has been proposed to eliminate the drive 1' by employing another means of torque transmission between the outer gear and the output shaft. Fluid pressure devices employing such substitutive torque transmission means are disclosed in U.S. Pat. No. 3,389,618 and West German Pat. No. 2,844,844. In one of the hydraulic motors proposed in such patents, the outer gear is directly coupled to the output shaft to make it rotatable in unison with the output shaft, while the inner gear is disposed for an orbital movement within a stationary ring member which is coaxial with the output shaft. In another known hydraulic motor, the inner gear is stationarily disposed coaxially with the output shaft, while the outer gear is disposed for orbital movement around a rotary member which is fixed to the output shaft. In order to realize the orbital movement of the inner gear or the outer gear, an inner gearing condition is maintained between the inner gear and the stationary ring or between the outer gear and the rotary member through a plurality of articulated holes formed therebetween and extending axially with each hole being formed partly in the confronting peripheries of the both members, and a plurality of cylindrically shaped rollers loosely disposed respectively in the holes.
The torque transmission through the holes and rollers, however, still suffers from the following disadvantages.
(1) The teeth profile does not perfectly meet the requirement in view of mechanics so that theoretical meshing condition cannot be achieved.
(2) Each hole consists of two arcuate portions so that the tooth height is small and the number of teeth held in any one meshing state at a time is impractically small.
(3) Generation of noise and vibration, as well as deterioration in the performance and life, is inevitable due to the disadvantages (2) stated above.